This invention relates to gas turbine engines and particularly to such engines having variable stator vanes in the engine compressor stage.
Typically, the compressor section of a gas turbine engine includes a row of stator vanes ahead of each row of compressor rotor blades to direct the intake air into the compressor rotor blades at an optimum angle of attack. In the more sophisticated engines, the stator vane angles are varied over the engine's operating envelope in an attempt to optimize performance for both design and off-design conditions.
As is well known, the angle of attack and aerodynamic characteristics vary from stage to stage of the compressor, and the rate of change of vane angle is therefore different for each row of vanes. Systems achieving this different rate of change are exemplified in U.S. Pat. Nos. 2,933,234 and 2,999,630 granted to R. E. Warren, L. V. C. Jensen, G. Neumann and F. E. Nagel on Sep. 12, 1961 and to G. Neumann on Apr. 19, 1960, respectively.
U.S. Pat. No. 4,279,568, granted to Alan D. Monroe on Jul. 21, 1981 describes a system wherein there is provided vane angle adjustment of all rows of stator vanes to follow a non-linear schedule. This system utilizes a vane angle actuator which is arranged to provide a non-linear schedule in response to engine speed for all rows of stator vanes. No attempt is made to adjust or change the approximately linear relation of each vane row angle to the angle of a reference vane row, i.e., to provide a non-linear relation between angle schedules for various vane rows.
A known arrangement for vane angle adjustment includes a pump handle adjustment lever which is pivotably mounted to a fixed portion of the engine at one end and interconnects to rows of adjustable vanes at selected points along its length, whereby there is a linear relation between the angular adjustment of each vane row and a given vane row, e.g., the inlet guide vane (IGV) vane row.
It is an object of the present invention to provide improved performance of a gas turbine engine by adjustment of the variation schedules for the stator vane angles. In particular it is an object of the invention to provide improved engine stall margin by such schedule adjustment.